Detect a Process

Looking for a bit of help / direction with this.

I have a command button,
If I press it I want it to see if calculator is open,
If it is open bring it on top.
if its not open then open calculator
End

I have this two bits of code so far
If calc is open this will bring it to the top
AppActivate ("Calc")


This opens calculator
Shell ("calc.exe") 'Opens sage selector program

I just don't know how to detect if calculator is already open. Then some sort of IF statement I guess?

any ideas?